Due to currently statutory provisions the particle emission of a combustion engine, in particular a diesel engine, before and/or after a particle filter, as for example a diesel particle filter (DPF), are monitored during the driving operation. Furthermore a load prognosis of the diesel particle filter is required for a regeneration control, in order to achieve a high system security and to be able to use more inexpensive filter material. Furthermore a regulation of the combustion features of the combustion engine can be provided on the basis of the information about the particle emission.
But particle filters provided a limited storage capacity for soot particles and have to be regenerated in certain intervals for restoring the purification effect. A controlling of the regeneration of the particle filter can take place either passively or actively. A high particle load of the filter causes an improperly high increase of the exhaust gas pressure.
In a simply, actively operated procedure a driven distance or an operating time of the combustion engine is usually referred to for the implementation of the regeneration of the filter in firm intervals. That takes place typically every 250 to 1000 km. a soot particle filters the regeneration takes place by an increase of the exhaust gas temperature up to typically 550° C. to 650° C. This can take place by measures in the mixture preparation of the engine or by post-engine measures. Thereby an exothermal reaction is activated, which causes a burn-off of the soot particle and which regenerates the particle filter within a few minutes (for example 20 minutes).
Thus a system is for example known from EP 1130227 A1 for supporting the regeneration of a particle filter that is arranged in an exhaust gas area of a combustion engine, at which the exhaust gas temperature is increased for starting and sustaining the particle regeneration by injecting hydrocarbons (HC) into the exhaust gas area. The increase of the exhaust gas temperature takes basically place by at least one fuel after-injection into the combustion engine, which causes an increased HC-concentration in the exhaust gas, which reacts exothermally in an oxidization catalyzer, which is arranged in streaming direction of the exhaust gas before the particle filter.
DE 102004031321 A1 and DE 102006009921 A1 suggest a procedure for metering a fuel into an exhaust gas duct of a combustion engine and a device for implementing the procedure.
Such a system, at which an accurately metered fuel amount is injected temporarily into the exhaust gas system for the regeneration of the particle filter, is also known under the name DEPARTRONIC and is particularly provided for the use in utility vehicles with diesel engines. The HC-measurement is determined from a period time and a duty cycle for controlling a shut-off valve and a metering valve within a fuel metering device, in order to meter a desired HC-mass flow into the exhaust gas system, whereby the calculated values are send to the corresponding device driver of the shut-off valve and the metering valve.
It has proven to be possibly problematic that the components of the HC-metering device create no autarchic system. The function rather depends for example on the pressure relations in the low-pressure circulation before the shut-off valve or before the metering valve. Furthermore the magnet force cannot suffice anymore for example at a low supply voltage and an increased coil temperature of the metering valve, in order to open the valve against higher difference pressures. A rudimentary diagnosing software would announce in that case a defect metering valve, even though it is technically working properly. Missing or too low heat removals, as for example due to a missing fuel or increased fuel temperature, can furthermore cause an overheating of the magnetic coil, whereby the coil can be destroyed in an extreme case.
It is therefore the task of the invention to establish a procedure, with which a maximally possible switching pressure can be determined at the metering valve, in order to ensure a secure switching of the metering valve, and which comprises only the previously mentioned influences. It is furthermore the task of the invention to provide a corresponding device.